Viscoelastic damping foam having an adhesive surface

ABSTRACT

The invention relates to a viscoelastic damping foam with an adhesive surface for adhesion coupling to vibrating surfaces, for solid-borne sound absorption. The viscoelastic damping foam is obtained through the stoichiometric reaction of a polyisocyanate with at least two polyols of the polyether type which are incompatible with one another.

The invention relates to a visco-elastic damping foam with an adhesivesurface for adhesion coupling to vibrating surfaces for solid-bornesound absorption.

Extremely varied polyurethane soft foamed materials are known forsound-insulation which, however, unlike the foamed material according tothe invention, are not suitable for sound deadening (anti-drumming).DE-AS 19 23 161 and DE-OS 28 35 329 describe foamed materials filledwith minerals which, because of their high density of 500 to 1,250kg/m³, enable good sound blocking. Sound-deadening (anti-drumming) ofsheet metal is, however, not possible with these materials since theloss factor of these foamed materials is too low.

DE-PS 27 56 622 focuses on the manufacture of foamed materials with highloss factors, but the method described, namely the impregnation ofopen-pored polyurethane foamed materials or PVC foamed materials withvisco-elastic materials, for example polyolefins containing inorganicfillers or organic resins or waxes, involves considerable outlay.

It is known from DE-OS 37 10 731.3 that polyurethane soft foamedmaterials with adhesive properties can be obtained when a polyisocyanateor a polyisocyanate prepolymer is reacted with polyols or mixturesthereof present in excess, whilst keeping an NCO index of ≦80. Thesub-cross-linking of isocyanate and polyol is used in order to arrive atthe desired surface properties. The foamed materials able to be producedaccording to this state of the art however have the disadvantage thatthe mechanical characteristic values turn out unfavourably as comparedto foamed materials based on two-component polyurethane which areproduced with the stoichiometric ratio.

Consequently the object of the invention is to provide a visco-elasticfoamed material, which is produced on the basis of polyurethane instoichiometrically balanced quantities of polyol and isocyanate with theusual additives. This visco-elastic foamed material produced thus hasadhesive surfaces for adhesion coupling to vibrating surfaces and hasthe required characteristics for sound-proofing. For the lining orcovering material itself, this concerns the loss factor d₂, according toDIN 53 440, and the modulus of elasticity E₂.

This object is achieved according to the invention in that theisocyanate is reacted in stoichiometric quantities with at least twopolyols, preferably of the polyether type, which are incompatible withone another. The two polyols are able to be mixed together, but onlybecause of their high viscosity or syrupy consistency. They are howeverincompatible with one another because they separate completely aftersome time. The process of separation occurs relatively slowly because ithas to “work” against the viscosity.

The polyether polyols used are characterised by a hydroxyl number ≦100and are produced on the basis of approximately 75% ethylene oxide in thepresence of a starter. Common polyether polyols are based for example on15 to 20% ethylene oxide. Mixtures of these two types of polyetherpolyol are incompatible with one another. Polyether polyols produced ona high ethylene oxide basis are used according to the state of the artas cell openers, at approximately 0.5% to 5% relative to the totalmixture. Compositions according to the present invention contain clearlygreater quantities in contrast to this, for example 50%.

The polyether polyol produced on a low ethylene oxide basis tends to bemore reactive than the polyol on a high ethylene oxide basis whichtherefore accumulates on the outer surfaces. The reaction in the foamedpart occurs in a stoichiometrically balanced manner. Nosub-cross-linking takes place, rather the adhesive surface is basedsurprisingly on the action of functional groups. The adhesivenessachieved according to the invention is produced with a functionality ofthe polyether polyol on a high ethylene oxide basis of 2 to 4.

In the exothermal reaction of polyols with isocyanate a highertemperature is produced, when filling the tool, in the inner core zonesof the part being produced than at the outer regions or on the surfaces.The heat quickly dissipates over the surface of the tool. Because of thelow temperature in the surface region of the foamed part being produced,the reaction speed is reduced there, as a result of which the separationof the at least two polyols which are incompatible with one anotherbegins.

Because of the necessary heat elimination the workpiece can only beheated to a moderate degree because the adhesive surfaces are nototherwise produced. Two exemplary formulae are found in the followingfor embodiments of the foam mixtures according to the invention. Theproduction of the products occurs preferably through the supply of thereaction components, the polyol system, on the one hand, and thepolyisocyanate system, on the other hand, into the mixing head of an RIM(Reaction Injection Moulding) unit.

Two different formulae were tested for the polyol system (component A),formula 1 with a high proportion of a polyether polyol on ethylene oxidebasis and formula 2 with a low proportion of the polyether polyol onethylene oxide basis. The reaction between component A and thepolyisocyanate (component B) was carried out in stoichiometricquantities as described above. Component A is composed as follows:

Component A: Formula 1 Formula 2 400 parts by weight 800 parts by weightDesmophen 3900 800 parts by weight 400 parts by weight Arcol 2580  40parts by weight  40 parts by weight Water  20 parts by weight  20 partsby weight DMEA 2.4 parts by weight 0.6 parts by weight Tegostab B 1400 8 parts by weight  8 parts by weight DABCO TD 100  16 parts by weight 16 parts by weight Dipropylene glycol

wherein

Desmophen 3900 is a polyether polyol based on propylene oxide with aproportion of approximately 18% ethylene oxide, a molecular weight of4800 and a hydroxyl number of 35;

Arcol 2580 is a polyether polyol based on ethylene oxide with aproportion of approximately 70% ethylene oxide, a starter for exampleTMP (=trimethylol propane), a molecular weight of 4000 and a hydroxylnumber of 42;

DMEA is the same as dimethyl ethylamine and is added as an adjuvant;

Tegostab B 1400 is a cell stabiliser and

DABCO TD 100 is the same as triethylene diamine and acts as a catalystfor cross-linking and foaming.

Component B

consists of diphenylmethane-4,4-diisocyanate with an NCO content of 28%,for example prepolymer Suprasec VM 27, but other isocyanates such as forexample raw MDI are also possible.

The stoichiometric ratio of A:B is 100 parts by weight A: 46 parts byweight B.

The ratio of polyether polyol based on propylene oxide relative to thepolyether polyol based on ethylene oxide is in the example 2:1 or 1:2.The formulae listed are. basic formulae, which can be altered inaccordance with the object to be achieved by the invention. The desiredadhesiveness of the foamed materials thus produced can be regulated bymeans of the proportion of Arcol 2580. The higher the proportion ofpolyether polyol on ethylene oxide basis, the greater the adhesivenessof the foamed material. As further tests have shown, the ratio of thepolyether polyol on propylene oxide basis relative to the polyetherpolyol on-ethylene oxide basis can be brought approximately to a weightratio of 5:1 to 1:5, as a result of which the adhesiveness can be finelygraded.

The desired adhesiveness of the foamed materials thus produced can beregulated by means of the proportion of the Arcol 2580, the higher theproportion of the polyether polyol on ethylene oxide basis, the greaterthe adhesiveness of the foamed material.

Sample bodies were taken from the foamed parts thus produced and testedwith regard to the physical-acoustic parameters. Values were found forthe loss factor d₂≧0.4 and for the modulus of elasticity E₂≦150,000N/m². The material density (specific gravity) is a secondaryconsideration, because it is substantially determined by the productionprocess and by the geometry of the mould. As a rough indicator value, itmay be that values between 60 and 150 kg/m³ appear for parts like thoseusually used for sound-proofing in the end wall-floor region of avehicle.

The application of the visco-elastic damping foams with adhesivesurfaces is not restricted to solid-borne sound damping of vibratingsurfaces, but extends to utilization as an acoustic spring element inso-called mass-spring systems on any vibrating and sound-emittingsurfaces. With greater layer thicknesses and particularly when used as aspring in the mass-spring system the airborne sound damping of thesurfaces for sound-proofing is increased.

What is claimed is:
 1. A viscoelastic damping foam having an adhesivesurface comprising a stoichiometric reaction product of a polyisocyanateand a polyol reactant, said polyol reactant consisting essentially of afirst polyether polyol based on propylene oxide and a second polyetherpolyol based on ethylene oxide, wherein said first and said secondpolyether polyols have hydroxyl numbers no greater than 100, and whereinsaid first polyether polyol and said second polyether polyol are presentin a weight ratio of from 5:1 to 1:5.
 2. A foam in accordance with claim1 wherein said first polyether polyol and said second polyether polyolare incompatible with each other.
 3. A foam in accordance with claim 1wherein said first polyether polyol is based on propylene oxide andcomprises between about 15% ethylene oxide and about 20% ethylene oxideand said second polyether polyol comprises between about 70% and about75% ethylene oxide.
 4. A foam in accordance with claim 3 wherein saidweight ratio of said first polyether polyol to said second polyetherpolyol is 2:1 to 1:2.
 5. A foam in accordance with claim 4 wherein saidfirst polyether polyol comprises about 18% ethylene oxide and saidsecond polyether polyol comprises about 70% ethylene oxide.
 6. A processfor absorbing solid-borne sound comprising adhesively coupling saidadhesive surface of said viscoelastic foam of claim 1 to a vibratingsurface.